1. Field of the Invention
The present invention relates to an ester wax used preferably in development of electrostatically charged images formed by electrophotography or electrostatic recording in a copier, a laser printer, etc, and to toner containing the wax.
2. Description of the Prior Art
The electrophotography technique used in copiers for business use or the like has been developed based on the electrophotography technique described in U.S. Pat. No. 2,297,691, Japanese Patent Publication (Tokko) Nos. 42-23910 and 43-24748. Electrophotography is a technique for forming visible images from image information via electrostatic latent images. More specifically, this technique includes the steps of attaching resin powder containing colored fine powder to electrostatic latent images formed on a photoreceptor to form toner images, transferring the toner images on a recording medium such as paper or OHP sheets, and fixing the toner images thereon by heating, pressing or other methods for a long time or semi-permanent fixation.
In recent years, high speed, compactness, color image formation, and low temperature fixation have been in demand for copiers, and in order to meet this demand, not only improvements in the apparatus of a copier but also a high performance toner for the apparatus have been in demand. In order to meet the requirements of energy saving laws that will be enacted in the future, the fixing temperature should be lowered to reduce power consumption of the entire apparatus, in particular, to reduce power consumption of a fixing apparatus, which is a challenge that should be inevitably achieved. From the viewpoint of prevention of environmental pollution, it is desirable that production of sublimates during heating is suppressed.
Recently, as a fixing process that can meet the above requirement, a roller fixing method that has good heat efficiency and can be realized in a compact mechanism or a flash fixing method that can be performed with high speed are used preferably.
However, in the flash fixing method, toner is momentarily subjected to a high temperature, so that more sublimates can be generated. In a heated roller fixing method, the surface of a heated roller is brought in contact with toner images on a paper sheet, and therefore a so-called offset phenomenon occurs in which toner is attached onto the surface of the heated roller, and transferred to a subsequently supplied recording medium, staining the images.
In order to prevent the offset phenomenon in the heated roller method, Japanese Laid-Open Patent Publication No. 57-37353 proposes use of a polyester resin having a three-dimensional network structure as a resin contained in toner. However, this kind of polyester resin includes unreacted hydroxyl groups or carboxyl groups in a molecule of the resin, so that if copying is repeated, the charge amount of the toner may vary significantly with ambient humidity. Therefore, a reduction of the image density or image staining such as a fog are caused, so that sufficient reliability cannot be obtained. Furthermore, Japanese Patent Publication (Tokko) Nos. 52-3304 and 52-3305, and Japanese Patent Publication No. 57-52574 propose a method for improving the releasing properties of the toner by blending polyethylene, polypropylene or the like as a releasing agent in the toner. However, if the toner contains these releasing agents, the melting point of the toner is increased, so that if fixation is performed at low fixing temperatures, a sufficient fixing strength on transfer paper cannot be obtained.
Another attempt is to use natural wax to improve the characteristics of the toner. For example, Japanese Laid-Open Patent Publication Nos. 1-185660, 1-185661, 1-185662, and 1-185663 propose a method of internally adding carnauba wax or montan wax to toner. However, these waxes usually contain free alcohols or free fatty acids in an amount of 10 wt % or more, and further contain a resin or a colored component, so that they do not have sharp melting characteristics. In particular, a component that melts at 55xc2x0 C. or less is present in the waxes, so that the surface portion of the toner is partially melted under storage conditions and in an environment for use, and thus, blocking of the toner occurs. In addition, the toner to which such ester wax is internally added has insufficient melting properties when heat is applied and has insufficient color reproducibility when original images are copied. The colored component present in the above-described waxes deteriorates the color reproducibility on OHP sheets, so that the toner containing such a wax cannot sufficiently meet the requirement of high image quality. Furthermore, in a flash fixing method, sublimates derived from impurities contained in the wax are produced during a fixing process, so that environmental pollution may be caused.
In recent years, instead of carnauba wax or montan wax, synthetic waxes having uniform quality and good supply stability have received attention. Japanese Laid-Open Patent Publication Nos. 7-98511, 8-50367, 8-50368, 8-297376, 11-160909, 2000-19768, and 2000-56505 and Japanese Patent Publication No. 2949558 use an ester compound obtained from a monohydric alcohol or polyhydric alcohol and saturated linear fatty acid as a wax for toner.
When synthesizing an ester, in order to minimize the acid value in the final product, alcohol has to be used excessively, and consequently, a raw material alcohol remains in the final product. On the other hand, in order to minimize the hydroxyl value, a fatty acid has to be used excessively, and consequently, a raw material fatty acid remains in the final product.
As described above, the synthetic ester waxes described in the above publications contain a raw material fatty acid or a raw material alcohol and further contain a catalyst for synthesis, so that they do not exhibit a sharp melting behavior. If toner contains such a synthetic ester wax, the anti-blocking properties, the storage stability and the anti-offset properties of the toner are insufficient. Furthermore, during toner kneading, the raw material fatty acid and the raw material alcohol in the wax are subjected to oxidation degradation, so that problems such as discoloring of the toner itself and odor generation are caused. Moreover, components produced by degradation of the raw material fatty acid and the raw material alcohol turn into sublimates, so that a filter for capturing them is clogged in a shorter time.
As described above, the conventional ester wax for toner does not act sufficiently as a releasing agent for toner, and is not sufficiently satisfactory in terms of reliability.
The present invention provides a synthetic ester wax that contains only a small amount of a raw material fatty acid and a raw material alcohol and has a sharp melting characteristic.
The present invention further provides toner containing the above ester wax so that it has anti-blocking properties and storage stability, and excellent color reproducibility, fixing properties and anti-offset properties.
As a result of in-depth study on the above-described problems, the inventors of the present invention found that since an ester wax that is synthesized by the use of a monocarboxylic acid and a monohydric or polyhydric alcohol having a specific number of carbon atoms and that has specific chemical properties has a sharp thermal melting behavior, the anti-blocking properties and the anti-offset properties can be improved and sublimates can be reduced by using this ester wax for toner, and thus the present invention has been attained.
An ester wax of the present invention is obtained by a condensation reaction of carboxylic acid and alcohol; wherein the carboxylic acid contains a single kind of saturated linear monocarboxylic acid having 14 to 30 carbon atoms as a main component, and the single kind of carboxylic acid is contained in a ratio of 60 wt % or more of the entire carboxylic acid; the alcohol contains a single kind of saturated linear monohydric alcohol having 14 to 30 carbon atoms or a single kind of polyhydric alcohol having 2 to 6 hydroxyl groups and having 2 to 30 carbon atoms as a main component, and when the monohydric alcohol is the main component, the monohydric alcohol is contained in a ratio of 60 wt % or more of the entire alcohol, and when the polyhydric alcohol is the main component, the polyhydric alcohol is contained in a ratio of 80 wt % or more of the entire alcohol; and the ester wax has an acid value of 3 mgKOH/g or less and a hydroxyl value of 5 mgKOH/g or less, and a maximum peak temperature in a differential thermal curve is in a range from 55xc2x0 C. to 90xc2x0 C.
In a preferred embodiment, in the differential thermal curve of the ester wax, 80% or more of a total peak area lies in a 10xc2x0 C. range between the maximum peak temperature minus 7xc2x0 C. and the maximum peak temperature plus 3xc2x0 C.
In a preferred embodiment, in the differential thermal curve of the ester wax, a peak area corresponding to a temperature region of xc2xe on the low temperature side of a peak area in a range from a melting start temperature to the maximum peak temperature is 35% or less of the total peak area.
In a preferred embodiment, a half band width of the maximum peak in the differential thermal curve of the ester wax is 5xc2x0 C. or less.
An ester wax of the present invention is obtained by a process comprising a condensation reaction of carboxylic acid and alcohol; wherein the carboxylic acid contains a single kind of saturated linear monocarboxylic acid having 14 to 30 carbon atoms as a main component, and the single kind of carboxylic acid is contained in a ratio of 60 wt % or more of the entire carboxylic acid; the alcohol contains a single kind of saturated linear monohydric alcohol having 14 to 30 carbon atoms or a single kind of polyhydric alcohol having 2 to 6 hydroxyl groups and having 2 to 30 carbon atoms as a main component, and when the monohydric alcohol is the main component, the monohydric alcohol is contained in a ratio of 60 wt % or more of the entire alcohol, and when the polyhydric alcohol is the main component, the polyhydric alcohol is contained in a ratio of 80 wt % or more of the entire alcohol; and the process comprises adding a hydrocarbon solvent to an esterified crude product obtained by the condensation reaction in a ratio of 5 to 100 parts by weight with respect to 100 parts by weight of the esterified crude product; and performing neutralization with an aqueous alkali solution.
In a preferred embodiment, the ester wax is obtained by a process comprising further adding an alcohol solvent having 1 to 3 carbon atoms in a ratio of 3 to 50 parts by weight with respect to 100 parts by weight of the esterified crude product, in addition to the hydrocarbon solvent, and performing neutralization with an aqueous alkali solution.
An ester wax of the present invention is obtained by a process comprising a condensation reaction of carboxylic acid and alcohol; wherein the carboxylic acid contains a single kind of saturated linear monocarboxylic acid having 14 to 30 carbon atoms as a main component, and the single kind of carboxylic acid is contained in a ratio of 60 wt % or more of the entire carboxylic acid; the alcohol contains a single kind of saturated linear monohydric alcohol having 14 to 30 carbon atoms or a single kind of polyhydric alcohol having 2 to 6 hydroxyl groups and having 2 to 30 carbon atoms as a main component, and when the monohydric alcohol is the main component, the monohydric alcohol is contained in a ratio of 60 wt % or more of the entire alcohol, and when the polyhydric alcohol is the main component, the polyhydric alcohol is contained in a ratio of 80 wt % or more of the entire alcohol; and the process comprises adding a water-soluble organic solvent to an esterified crude product obtained by the condensation reaction in a ratio of 3 to 50 parts by weight with respect to 100 parts by weight of the esterified crude product, and performing neutralization with an aqueous alkali solution; wherein the water-soluble organic solvent has a boiling point that is a temperature exceeding a melting temperature of the esterified crude product but not more than 300xc2x0 C., and has a specific gravity of 0.9 or more.
The present invention also includes a toner that comprises 100 parts by weight of a binding resin and 0.1 to 40 parts by weight of the above-mentioned ester wax.
Thus, the present invention described herein makes it possible to achieve the objects of (i) providing an ester wax that is obtained from a specific monocarboxylic acid and a specific alcohol and has specific thermal properties and chemical characteristics so that it can be used suitably in various fields; (ii) providing an ester wax that can be used preferably in a display device such as rewritable card and rewritable paper utilizing changes in the properties such as the optical transparency and the fluidity of the wax due to heat; a material for controlling electrical resistance in a thermo-sensor; a releasing material used in thermal transfer film; an adhesive that can effect peeling and adhesion repeatedly by changing the temperature; a developing material as typified by toner and the like; (iii) providing a toner containing the ester wax, in which blocking does not occur during storage so that it has excellent storage stability; and (iv) providing a toner that has excellent fixing properties, anti-offset properties and color reproducibility, good optical transparency of images fixed on an OHP film, and provides long term reliability to a copier, a printer or the like.